This study aims to prospectively investigate the local regional control, overall survival, treatment related toxicities and quality of life (QOF) of elderly stage I NSCLC patients receiving stereotactic ablative radiotherapy (SABR) with a moderate fractionation of 72 Gy/6 Gy/12 F (BED10 = 115 Gy). Patients' general characteristics, treatment modality, dose-volume histogram (DVH) parameters, toxicity profiling, quality of life, pattern of failure as well as survival time will be prospective recorded for the analysis.